Once

again, we may have to do with animals whose parts are
neither identical in form nor yet identical save for differences in
the way of excess or defect:
but they are the same only in the way
of analogy, as, for instance, bone is only analogous to fish-bone,
nail to hoof, hand to claw, and scale to feather; for what the feather
is in a bird, the scale is in a fish.